Apparatus has been developed to incrementally empty liquid-containing cylinders such as syringes. In one such apparatus, shown, for example, in U.S. Pat. No. 3,799,406, issued Mar. 26, 1974, a piston rod is incrementally advanced against a syringe. A one-way locking mechanism serves to connect a reciprocating actuator to the piston rod only during the advance of the actuator. A ball bearing is spring-biased against the piston rod to frictionally hold it in place at each incrementally-advanced position during the withdrawal movement of the reciprocating actuator.
The disadvantage, however, of such apparatus is that, because it has no means for automatically resetting the piston rod at the end of the cycle, resetting has to be done by hand. That is, when an unlocking sleeve is pushed against the locking mechanism, the piston rod has to be manually pulled against the ball bearing, to its initial position. Such a technique is inconvenient and cumbersome.